The joint prosthesis at which the attachment and connecting members according to the invention are configured for use, comprises two attachment members, of which one is configured for attachment to the second metacarpal bone and the other to the first metacarpal bone at a thumb joint, and a connecting member for connecting the two attachment members to each other. The attachment member for the second metacarpal bone comprises a screw-like part and the attachment member for the first metacarpal bone may comprise a screw-like part. These screw-like parts are adapted for being attached by screwing into the respective bone. The attachment members for the first and second metacarpal bones also comprise members for connecting the screw-like parts of the attachment members to the connecting member.
The above-mentioned type of joint prosthesis is configured for use as a primary replacement at thumb joints when the trapezium is not suitable for implantation, as an intra-operative salvage procedure when the trapezium is fractured and not suitable for implantation, as a salvage procedure after total trapezectomy or partial trapezectomy or other hemiarthroplasty or total replacement of another joint prosthesis or as a revision implant after loosening or failure of the screw-like part and/or the articulated socket element in the trapezium, i.e. for use after complete removal of the trapezium. The above-mentioned type of thumb joint prosthesis is configured for use also in patients having osteoarthritis, irrespective of the quality of the trapezium. The joint prosthesis is thereby replacing the normal interposition technique/conservative treatment.
At carpometacarpal thumb joint prosthesis, the attachment member for the second metacarpal bone is subjected to substantial bending and distraction forces, while the attachment member for the first metacarpal bone is subjected to substantial compression forces. It is important that the thumb joint prosthesis can be configured such that these forces can be met in order to achieve an effective and reliable joint prosthesis, i.e. the joint prosthesis can be configured to resist particularly said bending and distraction forces without breaking or loosening of any of its components.